Use of guanidinium salts of unsaturated fatty acids as corrosion inhibitors

ABSTRACT

A method for the temporary protection of metal surfaces from corrosion is provided in which the metal surface to be temporarily protected from corrosion is coated with a guanidinium salt of an unsaturated fatty acid containing 6 to 44 carbon atoms.

FIELD OF THE INVENTION

This invention relates to oil-based corrosion inhibitors for metallicsurfaces, more particularly iron-based surfaces, which are preferablyused in the form of oil-in-water emulsions. The invention providesalkylamine-free corrosion inhibitors which are distinguished by good oilsolubility and which, at the same time, emulsify the oil phase in water.

RELATED ART

Rust-control emulsions are used for temporarily protecting metalsagainst atmospheric corrosion-inducing influences. They essentiallycontain nonpolar or polar oils, emulsifiers, corrosion inhibitors andwater. Their effect is based on the adsorption of inhibitor molecules tothe metal surface and on the formation of a protective film of emulsioncomponents which acts as a diffusion barrier against atmospheric oxygenand water. In "Oberflache-Surface" 1989, No. 4, pages 8-12, T. Forsteret al. report on modes of action of and tests for rust-controlemulsions.

Conventional corrosion-control formulations contain such components as,for example, petroleum sulfonates, salts of alkyl sulfonamidocarboxylicacids and amine or other salts of partial esters of alkyl or alkenylsuccinic acid. For example, EP-A-566 956 describes corrosion-controlformulations based on an amine-free salt of a semiester of an alkyl oralkenyl succinic acid.

Sulfur-containing corrosion inhibitors such as, for example, alkyl arylsulfonic acids, petroleum sulfonates or salts of alkylsulfonamidocarboxylic acids have the disadvantage that they can readilybe degraded by micro-organisms, such as sulfur-reducing bacteria, whichcan lead to serious odor emission problems. Alkylamine-containingcorrosion-control formulations, particularly those containing secondaryamines, are attracting increasing criticism on account of the risk ofthe formation of health-endangering nitrosamines. Accordingly, there isa need for sulfur-free and alkylamine-free corrosion inhibitors. Stearicacid derivatives have been described as corrosion inhibitors for purelyoil-based systems, for example lubricating oils and lubricating greases(DE-C-32 03 491). Examples of the stearic acid derivatives in questionare 9,10-dihydroxystearic acid and alkali metal salts and oligomericcondensates thereof, 9,10-epoxystearic acid, alkali metal salts andoligomeric "Estolids" thereof and, finally, mixed oligomers of9,10-epoxy and 9,10-dihydroxystearic acid.

Corrosion-control formulations intended to be used in the form ofoil-in-water emulsions may be marketed as purely oil-based, i.e.water-free, concentrates so that they may be brought into theready-to-use emulsion form by addition of water at the point of use.These oil concentrates contain the corrosion inhibitors which,accordingly, have to be oil-soluble. To ensure that the oil concentratesare able spontaneously to form an emulsion on dilution with water, i.e.are self-emulsifying, it has hitherto been necessary for theconcentrates to contain emulsifiers in addition to the corrosioninhibitors. Possible interactions between the surface-active emulsifiersand the polar corrosion inhibitors often have an adverse effect onemulsifying behavior and on the corrosion-control effect and, as aresult, complicate formulation of the product. This problem could beeliminated if oil-soluble corrosion inhibitors with emulsifyingproperties could be made available.

Guanidinium salts of unsaturated fatty acids and processes for theirproduction are known from U.S. Pat. No. 2,978,415. These guanidine soapsof unsaturated fatty acids are used as so-called boosters in thecleaning of textiles with solvents, i.e. in dry cleaning. Acorrosion-inhibiting effect and emulsifying power are of no significancefor this particular application which takes place in purely organicphase. Accordingly, the US patent in question does not contain any dataon a corresponding effect of the guanidine soaps of unsaturated fattyacids.

BRIEF DESCRIPTION OF THE INVENTION

The problem addressed by the present invention was to provide newsulfur-free and alkylamine-free corrosion inhibitors of which oilsolutions would not have unacceptably high viscosities, even at highactive-substance concentrations, and which at the same time wouldemulsify the oil phase on the addition of water without any need foradditional emulsifiers to be used.

This problem has been solved by the use of guanidinium salts of mono- orpolyunsaturated fatty acids containing 6 to 44 carbon atoms forobtaining temporary protection against corrosion on metal surfaces,preferably iron-based surfaces.

DETAILED DESCRIPTION OF THE INVENTION

In the context of the invention, fatty acids are understood to becarboxylic acids which may optionally be OH-substituted. The unsaturatedfatty acids suitable for use in accordance with the invention may bedivided into two groups, namely: native fatty acids, which occur as acomponent of natural oils and fats, and so-called dimer fatty acidswhich are obtainable by generally acid-catalyzed dimerization ofsaturated fatty acids. Accordingly, the unsaturated fatty acids suitablefor use in accordance with the invention are characterized on the onehand in that they represent native fatty acids, i.e. are branched or,preferably, linear, have 1 to 6 and preferably 1 to 3 double bonds andcontain preferably 11 to 28 and, more preferably, 18 to 22 carbon atoms.Suitable unsaturated fatty acids of this type are preferably monobasicand are selected, for example, from undecylenic acid, myristoleic acid,palmitoleic acid, oleic acid, ricinoleic acid, erucic acid, linoleicacid, linolenic acid, arachidonic acid and mixtures thereof. On theother hand, unsaturated fatty acids from the group of so-called dimeracids are also suitable. These acids are polybasic and preferablydibasic. Dimer acids containing 36 to 44 carbon atoms are particularlysuitable.

Guanidinium salts of defined pure fatty acids may be used with advantagefor the purpose according to the invention. For economic reasons,however, guanidinium salts of technical fatty acid mixtures which maycontain certain amounts of saturated fatty acids in addition tounsaturated fatty acids differing in their carbon chain lengths will beused in practice. Technical fatty acid mixtures such as these may beobtained, for example, by the hydrolysis of suitable natural oils andfats. For the use according to the invention, however, at least 50% byweight and preferably at least 80% by weight of the technical fatty acidmixtures must consist of unsaturated fatty acids with the carbon chainlengths mentioned.

The so-called dimer fatty acids which may also be used in accordancewith the invention are generally not pure substances either, but maycontain fatty acids differing in their carbon chain lengths and/or theirdegrees of oligomerization. Besides the actual dimer fatty acids,trimerization or polymerization products, for example, may be presentalongside unreacted and/or isomerized monomer fatty acids. Dimer fattyacids in the context of the invention are understood to be productmixtures of which at least 50% by weight and preferably at least 70% byweight consist of dimer fatty acid with a carbon chain length of 36 to44. Products such as these are commercially available, for example fromthe Unichema under the product group name of Pripol® or from Henkel KGaAunder the product group name of Empol®.

For their use in accordance with the invention, the guanidinium salts ofthe above-mentioned fatty acids are employed as solutions inhydrocarbons liquid at the working temperature, substantiallywater-insoluble dialkyl ethers and/or acetals and mixtures thereof.Other oil phases suitable for dissolving the guanidinium salts ofunsaturated fatty acids are ester oils such as, for example, oleyloleate, products of the esterification of aliphatic dicarboxylic acids(preferably C₈₋₉) with branched Guerbet alcohols (preferably C₁₂₋₂₀)(EP-A-489 809), esters of C₁₋₅ monocarboxylic acids with monohydric orpolyhydric alcohols (described, for example, in DE-A-39 07 391), estersof C₆₋₁₁ monocarboxylic acids with monohydric or polyhydric alcohols(described, for example in DE-A-39 07 392) and products of thealkoxylation of triglycerides with 0.5 to 3 moles of EO and/or PO, forexample glycerol propoxylate trioleate (German patent application P 4323 771). Also suitable are substantially water-insoluble saturated orunsaturated C₆₋₃₆ fatty alcohols which are liquid at the workingtemperature. In their case, both simple alcohols and α, ω-diols may beused.

These essentially water-insoluble solvents are referred to hereinafteras "oil-like solvents".

Solutions containing between 1 and 45% by weight of dissolvedguanidinium salts of unsaturated fatty acids are preferably used. Withlower contents, there is a distinct reduction in thecorrosion-inhibiting effect whereas, with higher contents, the solutionsgenerally become so highly viscous that their handling and their use foremulsion formation are unnecessarily complicated. However, higherconcentrations may also be used for the purposes of the inventionproviding the attendant difficulties of emulsion formation are accepted,for example preliminary heating of concentrate and mixing water and theuse of technical emulsification aids, for example high-speed tootheddisks or ultrasound.

Suitable oil-like solvents for the guanidinium salts of unsaturatedfatty acids are, for example, hydrocarbons which are liquid at theworking temperature, i.e. at a temperature of about 10 to about 90° C.Examples of such hydrocarbons are paraffin oil or mineral oil. In thelatter case, low-aromatic mineral oils are preferred for ecological andtechnological reasons. Suitable oils of this type are commerciallyavailable and include, for example, Pionierol 4556, a product of Hansen& Rosenthal, Enerpar 3036, a product of Deutsche BP, and Parex ParaffinII, a product of Leuna-Werke.

Other suitable oil-like solvents for the guanidinium salts ofunsaturated fatty acids are substantially water-insoluble dialkyl etherswhich are liquid at the working temperatures mentioned above. By"substantially water-insoluble" are meant dialkyl ethers of which nomore than 5% by weight and preferably no more than 0.5% by weightdissolve in water. Suitable examples are dialkyl ethers containing 6 to24 and preferably 8 to 18 carbon atoms per alkyl group, the alkyl groupsindependently of one another being linear or branched, saturated orunsaturated and preferably being n-octyl, 2-ethyl-hexyl, stearyl and/orisostearyl groups. The dialkyl ethers may contain free hydroxyl groups,in which case they are referred to as hydroxy mixed ethers. The use ofsuch dialkyl ethers in liquids for treating metals is described, forexample, in German patent application P 42 37 501. Dialkyl ethers of thetype in question are commercially available, for example from HenkelKGaA under the name of Cetiol-OE (dioctyl ether).

Other suitable oil-like solvents for the use of the guanidinium salts inaccordance with the invention are acetals based on monofunctionalaldehydes containing 1 to 25 and preferably 1 to 10 carbon atoms andmonohydric alcohols containing 1 to 25 and, more particularly, 2 to 20carbon atoms. The use of such acetals as a mineral oil substitute, as anoil component or as a base oil in lubricating oils and in liquids fortreating metals is known from EP-A-512 501. A general process for theproduction of such acetals is also disclosed in this document.

For their use in accordance with the invention, the guanidinium salts ofunsaturated fatty acids are preferably used in the form of a solution inone of the oil-like solvents mentioned above or in mixtures thereof asthe oil phase of an oil-in-water emulsion. The oil phase, i.e. thesolution of the guanidinium salts of the unsaturated fatty acids,preferably makes up from 0.5 to 50% by weight and more preferably from 5to 20% by weight of the emulsion. A rule of thumb in this regard is thatthe quantity of oil phase present can be smaller, the higher theconcentration of the guanidinium salts of unsaturated fatty acids in theoil phase. Good corrosion control results are obtained, for example,when an oil-in-water emulsion containing 10% by weight of oil phase isused, the oil phase having a concentration of a guanidinium salt of anunsaturated fatty acid, for example guanidinium oleate, of 5 to 20% byweight.

By adding glycols, the viscosity of the solutions of the guanidiniumsalts of unsaturated fatty acids in the oil-like solvents can beadjusted to applicationally favorable values without their ability toform an emulsion with water being influenced in any way. Suitableglycols are, for example, butyl diglycol, hexylene glycol or dipropyleneglycol which may be added to the guanidinium salt solution in quantitiesof 1 to 10% by weight. The glycols may be added either to the solutionof the guanidinium salts of unsaturated fatty acids in oil-like solventsor to the oil-like solvent before the reaction of guanidinium salts ofvolatile acids with unsaturated fatty acids described in the following.By virtue of its favorable effect on corrosion control, hexylene glycolis preferably used.

The present invention also relates to the oil-in-water emulsionssuitable for the use of guanidinium salts of unsaturated fatty acids inaccordance with the invention. However, the suitability of suchemulsions for use in the treatment of metals goes beyond this particularapplication. For example, the emulsions may be used as cooling lubricantemulsions in the machining of metals, in which case the emulsions maycontain other active substances known for this particular application,including for example lubrication-enhancing additives or biocides.

Accordingly, the present invention also relates to oil-in-wateremulsions of which the oil phase is an oil-like solvent or solventmixture and contains the guanidinium salts of unsaturated fatty acids indissolved form in concentrations of 1 to 45% by weight and preferably 5to 20% by weight, based on the oil phase, the oil phase making up from0.5 to 50% by weight and preferably from 5 to 20% by weight of theemulsion.

The emulsions are preferably prepared by mixing a solution of theguanidinium salts in the oil-like solvent with water. Since theguanidinium salts are soluble both in the oil-like solvents and inwater, they are distributed between the water phase and the oil phase.In each individual case, the distribution equilibrium depends upon theoil-like solvent selected and upon the type of the unsaturated fattyacid. As described in Example 11, an emulsion can also be obtained byemulsifying an aqueous solution of the guanidinium salts with oil. Inthis case, too, a distribution equilibrium of the guanidinium salts canbe expected to be established.

The oil phase containing the guanidinium salts of unsaturated fattyacids in at least partly dissolved form makes up about 0.5 to about 50%by weight and preferably about 5 to about 20% by weight of theoil-in-water emulsion. An emulsion such as this is normally stablewithout other co-emulsifiers for the periods of several hours requiredfor application. In special cases, for example where the emulsioncontains other active substances, for example builder salts, orimpurities arising out of its use, the emulsion may have to bestabilized by the use of additional co-emulsifiers. Suitableco-emulsifiers are nonionic surfactants, more particularly ethoxylationproducts of fatty alcohols, for example a product of the addition of 6moles of ethylene oxide to 1 mole of a C_(12/14) fatty alcohol mixture,or anionic emulsifiers, for example alkyl benzene sulfonates. Thenecessary quantities are determined by the other components of theemulsion and have to be determined by tests. The use of up to 20% byweight of co-emulsifier, based on the quantity of the oil solution, maybe taken as a guide value.

The emulsion may be present in the form of a conventional milky toopaque emulsion. For special applications, it can also be of advantageto use the emulsion in the form of an almost transparent so-calledmicro-emulsion with an oil content of up to 50% by weight of the typeobtainable by phase inversion from a water-in-oil emulsion. This phaseinversion, which can be induced for example by varying the temperature,is also known as the PIT (phase inversion temperature) method. It isdescribed in detail in German patent application P 43 23 908. A variantof this process is described in Example 11 below.

The production of the guanidinium salts of unsaturated fatty acids isdescribed in U.S. Pat. No. 2,978,415 which was cited earlier on. Forexample, a mixture of unsaturated fatty acids may be dissolved in anorganic solvent, such as methyl isobutyl ketone, and guanidiniumcarbonate may be added to the resulting solution. On completion of thereaction, which is accompanied by the elimination of water and CO₂, boththe solvent and the water of reaction may be removed, the productremaining behind in the form of a brown wax-like paste. For the useaccording to the invention, it is advisable to use volatile acids, forexample guanidinium carbonate, as solvents for the reaction of theunsaturated fatty acids with guanidinium salts and directly to employoil-like solvents as the oil-phase to be used for the subsequentformation of the emulsion. A corresponding production example isdescribed in the following.

Depending on the oil-like solvent used, it can be advisable to removethe water of reaction formed during the reaction of guanidiniumcarbonate with the fatty acid more or less completely from the reactionproduct because the viscosities of the solutions obtained can depend toa large extent upon their water content. The optimal productionprocedure (heating, application of vacuum) depends on the one hand uponthe unsaturated fatty acid or fatty acid mixture used and, on the otherhand, upon the oil-like solvent used and has to be empiricallydetermined for each particular case.

It is of advantage, when preparing the solutions of guanidinium salts ofunsaturated fatty acids in the oil-like solvent, to obtain homogeneousliquids of which the viscosity enables them to be allowed to run intowater without any need for other technical emulsion-forming measures.Highly viscous paste-like systems are more difficult to handle and,accordingly, are less preferred. Guanidinium salts of saturated fattyacids which are known as corrosion inhibitors are unsuitable for the useaccording to the invention because their oil solutions in theconcentration ranges according to the invention are wax-like pastesrather than free-flowing liquids.

EXAMPLES Example 1

This Example describes the preparation of a guanidinium oleate solutionin mineral oil containing 38% by weight of the salt in accordance withU.S. Pat. No. 2,978,415. In a heatable stirred reactor with a nitrogeninlet, 610.6 g of technical oleic acid with an acid value of 202(Edenor® TiO5GA, Henkel KGaA, Dusseldorf), corresponding to 2 moles+10%excess, are mixed with 1096 g of mineral oil (Pionierol 4556, Hansen &Rosenthal). 180 g (1 mole) of guanidinium carbonate (Linz Chemie, Linz,Austria) are introduced in portions with stirring at room temperatureunder a nitrogen blanket. After the addition, the reaction mixture isheated to 100° C. and stirred until the acid value is below 20 (about 2hours). During the reaction, there is a slight evolution of gas and thesolution changes color from light yellow to beige-brown. Theoretically,the elimination of 1 mole of carbonic acid corresponding to 1 mole of H₂O and 1 mole of CO₂, 62 g, is expected during the reaction. Ahigh-viscosity, beige-brown, transparent oil solution is obtained as thereaction product.

Examples 2 to 4

Production was carried out in exactly the same way as in Example 1except that the solvent was varied.

Example 2

Solvent: paraffinic process oil Enerpar 3036, Deutsche BP

Example 3

Paraffin oil Parex Paraffin II, Leuna-Werke

Example 4

Solvent, dioctyl ether Cetiol OE, Henkel KGaA.

Brown, transparent, high-viscosity but free-flowing liquids wereobtained in every case.

Example 5

This Example describes the production of a guanidinium oleate solutionin mineral oil containing 10% by weight of the salt in accordance withU.S. Pat. No. 2,978,415. In a heatable stirred reactor with a nitrogeninlet, 638 g of technical oleic acid with an acid value of 202 (Endenor®TiO5GA, Henkel KGaA, Dusseldorf), corresponding to 2 moles+15% excess,were mixed with 190 g of mineral oil (Pionierol 4556, Hansen &Rosenthal). 180 g (1 mole) of guanidinium carbonate (Linz Chemie, Linz,Austria) were introduced in portions with stirring at room temperatureunder a nitrogen blanket. After the addition, the reaction mixture isheated to 100° C. and stirred until the acid value is below 20 (about 2hours). During the reaction, there is a slight evolution of gas and thesolution changes color from light yellow to beige brown. After the mainreaction, a water jet vacuum is applied (for 15 mins.) at 100° C. toremove CO₂ and water. The reaction mixture is diluted with 6620 g ofmineral oil. A beige-brown transparent oil solution, from whichemulsions can be prepared by addition of 90% by weight of water, isobtained as the reaction product.

Examples 6 to 10, Comparison Examples 1 to 3

The corrosion-inhibiting effect was tested by the condensation testaccording to DIN 50017 KFW. To this end, 5 cm×10 cm steel plates of thequality ST 1405 were brushed with an aqueous surfactant solution, rinsedwith water and alcohol and dried. The plates were then immersed in oilsolutions according to Examples 1 to 5. 20% by weight solutions of BaPetronate 70 TBN (Witco) in oils according to the Table were used asComparison Examples 1 to 3.

The test cycle began after a drainage time of 24 hours, the test platesbeing inspected daily for corrosion. The results are set out in theTable where "traces of corrosion" means that there are at most 3corrosion spots on the surface, "slight corrosion" means that less than20% of the surface is corroded and "serious corrosion" means that morethan 20% of the surface is corroded.

                  TABLE                                                           ______________________________________                                        Corrosion Control Test -- Condensation Test                                   According to DIN 50017 KFW                                                    Test                                                                          Substance      Results                                                        ______________________________________                                        Example 6                                                                             Product of Up to 13 days, no corrosion                                        Example 1  Up to 24 days, traces of corrosion                                            After 25 days, terminated with slight                                         corrosion                                                  Example 7                                                                             Product of After 25 days, terminated without any                              Example 2  corrosion                                                  Example 8                                                                             Product of Up to 16 days, no corrosion                                        Example 3  After 25 days, terminated with traces of                                      corrosion                                                  Example 9                                                                             Product of Up to 15 days, no corrosion                                        Example 4  After 25 days, terminated with traces of                                      corrosion                                                  Example 10                                                                            Product of Up to 7 days, no corrosion                                         Example 5  After 20 days, serious corrosion                           Comp. 1 Barium petro-                                                                            After 1 day, serious corrosion                                     leum sulfonate                                                                           (>20% corroded)                                                    in Pionierol                                                                  4556                                                                  Comp. 2 Barium petro-                                                                            Up to 2 days, no corrosion                                         leum sulfonate                                                                           Up to 3 days, traces of corrosion                                  in Enerpar After 5 days, terminated with serious                              3036       corrosion                                                  Comp. 3 Barium petro-                                                                            Up to 1 day, traces of corrosion                                   leum sulfonate                                                                           After 5 days, terminated with serious                              in Parex Paraf-                                                                          corrosion                                                          fin II                                                                ______________________________________                                    

Production and corrosion-inhibiting effect of emulsions The products ofExamples 1 to 5 were diluted with deionized water in a ratio by weightof 1:9. Stable emulsions were obtained. By contrast, no emulsions wereformed when solutions of barium petroleum sulfonate in oils were addedin accordance with Comparison Examples 1 to 3.

The corrosion-inhibiting effect of an emulsion obtained by adding waterto the product of Example 5 in a ratio by weight of 1:9 was tested as inExample 10. After 7 days, no corrosion was observed; after 20 days,serious corrosion was observed.

Viscosity regulation

To adjust the viscosities of the products of Examples 1 to 5, glycols(for example butyl diglycol, hexylene glycol, dipropylene glycol) wereadded to them in quantities of 5% by weight. The formation of emulsionson addition of water in a ratio by weight of 1:9 was not affected.

For corrosion testing as in Example 10, the product of Example 5 wasmixed with 5% by weight of hexylene glycol. An emulsion was obtained byadding water in a ratio by weight of 1:9 and was used to test thecorrosion-inhibiting effect. Result: no corrosion after 8 days, seriouscorrosion after 13 days.

Example 11

Production of a microemulsion by phase inversion

In a first step, solvent-free guanidinium oleate was prepared by mixing90 g (=0.5 mole) of guanidinium carbonate with 281 g (=1 mole) oftechnical oleic acid, acid value 202 (Edenor® TiO5, Henkel KGaA,Dusseldorf) at room temperature in a stirred reactor. The temperaturewas increased to 150° C. over a period of 45 minutes with stirring andwas left at that level for 3.5 hours. A yellow-brown wax-like productwith an acid value of 5 was obtained.

To prepare a microemulsion by the phase inversion method, 2.6 parts byweight of this guanidinium oleate and 0.26 part by weight of sodiumcitrate were dissolved in 51.04 parts by weight of water. The solutionwas mixed while stirring with 40 parts by weight of mineral oil(Pionierol 4556) and 6.1 parts by weight of emulsifier (product of theaddition of 4 moles of ethylene oxide to a C_(12/14) fatty alcoholmixture) at a temperature above the phase inversion temperature of 35°C. determined in preliminary tests and was cooled to below the phaseinversion temperature. A transparent microemulsion was obtained andcould be diluted by adding water.

We claim:
 1. A method for protection of metal surfaces from corrosionwhich comprises applying to the metal surface to be protectedguanidinium salts of unsaturated fatty acids containing 6 to 44 carbonatoms.
 2. The method claimed in claim 1, wherein the unsaturated fattyacids comprise at least one member selected from the group consisting ofnative fatty acids and dimer fatty acids.
 3. The method claimed in claim2, wherein the native fatty acids comprise branched or linear fattyacids, having 1 to 6 double bonds and containing 11 to 28 carbon atoms.4. The method claimed in claim 3, wherein the native fatty acidscomprise a member selected from the group consisting of undecylenicacid, myristoleic acid, palmitoleic acid, oleic acid, ricinoleic acid,erucic acid, linoleic acid, linolenic acid, arachidonic acid andmixtures thereof.
 5. The method claimed in claim 2, wherein the dimerfatty acids are polybasic acids containing 36 to 44 carbon atoms.
 6. Themethod claimed in claim 1 wherein the guanidinium salts comprise aliquid solution in an essentially water-insoluble solvent selected fromthe group consisting of hydrocarbons liquid at the working temperature,substantially water-insoluble dialkyl ethers, substantiallywater-insoluble alcohols, substantially water-insoluble ester oilssubstantially water-insoluble acetals and mixtures thereof, inconcentrations of 1 to 45% by weight.
 7. The method claimed in claim 6,wherein the dialkyl ethers comprise alkyl groups which independently ofone another are linear or branched, saturated or unsaturated groups andeach alkyl group contains 6 to 24 carbon atoms.
 8. The method claimed inclaim 6, wherein the solvent for the guanidinium salts comprises atleast one acetal based on a monofunctional aldehyde containing 1 to 25carbon atoms and a monohydric alcohol containing 1 to 25 carbon atoms.9. The method claimed in claim 6, wherein the solvent for theguanidinium salts comprises at least one member selected from the groupconsisting of paraffin oil and mineral oil.
 10. The method claimed inclaim 1 wherein the guanidinium salts of unsaturated fatty acids aredissolved in an oil-in-water emulsion, comprising an essentiallywater-soluble solvent comprising an oil phase, the oil phase comprisingfrom 0.5 to 50% by weight of the emulsion and the guanidinium saltscomprising from 1 to 45% by weight of the oil phase.
 11. An oil-in-wateremulsion comprising an oil phase comprising an essentiallywater-insoluble solvent comprising guanidinium salts of unsaturatedfatty acids in dissolved form at a concentration of 1 to 45% by weightbased on the weight of the oil phase, the oil phase comprising from 0.5to 50% by weight of the emulsion.
 12. An oil-in-water emulsion asclaimed in claim 11, wherein the emulsion is a microemulsion formed byphase inversion.
 13. The method of claim 10 wherein the solventcomprises a liquid selected from the group consisting of hydrocarbons,substantially water-insoluble dialkyl ethers, substantiallywater-insoluble alcohols, substantially water-insoluble ester oils,substantially water-insoluble acetals and mixtures thereof.
 14. Themethod of claim 13, wherein the unsaturated fatty acids comprise atleast one member selected from the group consisting of native fattyacids and dimer fatty acids.
 15. The method of claim 14, wherein thenative fatty acids comprise branched or linear fatty acids, having 1 to6 double bonds and containing 11 to 28 carbon atoms.
 16. The method ofclaim 15, wherein the native fatty acids comprise a member selected fromthe group consisting of undecylenic acid, myristoleic acid, palmitoleicacid, oleic acid, ricinoleic acid, erucic acid, linoleic acid, linolenicacid, arachidonic acid and mixtures thereof.
 17. The method of claim 13,wherein the dimer fatty acids are polybasic acids containing 36 to 44carbon atoms.
 18. The method of claim 17, wherein the dialkyl etherscomprise alkyl groups which independently of one another are linear orbranched, saturated or unsaturated groups and each alkyl group contains6 to 24 carbon atoms.
 19. The method of claim 13, wherein the solventfor the guanidinium salts comprises at least one acetal based on amonofunctional aldehyde containing 1 to 25 carbon atoms and a monohydricalcohol containing 1 to 25 carbon atoms.
 20. The method of claim 14,wherein the solvent for the guanidinium salts comprises at least onemember selected from the group consisting of paraffin oil and mineraloil.